Why are some buttons purple?
By pressing D over an input field you are telling Blender to create a driver for that value. A driver is a way of controlling one value (the driven value) by another value (the driver). For example you  could drive the scale of one object by the rotational value of another.

To remove the driver you can either right-click on the value and choose 'Delete Drivers' or you could:

Navigate to the 'Graph Editor' from any screen area:



Change the view from 'F-Curve' to 'Drivers':



Shift select all the driven channels in the list and press X to delete them:



If you want to view and delete drivers for multiple objects at the same time make sure to toggle off the cursor icon which limits the view to currently selected objects: